In a manufacturing process of a semiconductor wafer and a flat panel display such as a liquid crystal display (LCD), a plasma display panel (PDP) and an organic light emitting diode (OLED), there is need of inspecting whether a unit process is successfully performed or not every time when each process is finished.
For example, a method for inspecting a defect such as a foreign material, a protruding part or a recessed part on a substrate, a method for inspecting a pattern on the substrate besides the defect, etc. are widely used in an LCD manufacturing process. As one of the methods for inspecting the defect or the pattern on the substrate, there is a dark field inspection method. Here, a subject to be inspected includes an object to be directly inspected, i.e., the foreign material or the pattern, and a base like a mirror.
FIG. 1 is a schematic view of a conventional dark-field inspection apparatus.
Referring to FIG. 1 the dark-field inspection apparatus is an apparatus for inspecting a subject 2 on a base 1, for example, a foreign material laid on a glass substrate, or a protruding part or a recessed part formed on a glass substrate. An illuminating unit 10 is arranged to emit light a1, a2 toward the subject 2 on the base 1. The light a1, a2 emitted from the illuminating unit 10 is reflected or scattered by the subject 2 such as a protruding part or reflected by the base 1 such as a glass substrate. Some light all of the light reflected and scattered by the subject 2 enter an image sensing unit 20 placed above the base 1, and thus the image sensing unit 20 uses the incident light a11 to sense an image of the subject 2. The image sensed by the image sensing unit 20 is analyzed in an image processing unit 30, so that it is possible to determine whether the subject 2 exists on the base 1 or which kind of the defect the subject 2 belongs to.
While some of the light a1, a2 emitted from the illuminating unit 10 are reflected and scattered by the subject 2 and travel toward the image sensing unit 20 (refer to a11), another some are reflected and scattered by the subject 2 and travel not to the image sensing unit 20 (refer to a12) or likewise reflected by the base 1 and travel not to the image sensing snit 20 (refer to a22). Thus, the light a12, a22 traveling not to the image sensing unit 20 wastes, so that a capacity light of the illuminating unit 10 is not fully used for sensing the image of the subject 2. Further, since the illuminating unit 10 emits the light in a certain direction, there arises a problem in that only a certain surface of the subject 2 is highlighted when sensing an image.